Reverse breathing is common in CMA. I use it frequently in Tai Chi Chuan practice. I'm not a Kenpo person, but I understand that Kenpo has its roots in CMA and so I wouldn't be surprised if it showed up there as well. It's a reasonably natural movement to exhale and expand when striking outward (which is consistent with reverse breathing), so I would bet that many people do it instinctively when fighting without even realizing they're doing it.
You say you use it in Tai Chi, for what and to what end? Have you conscienously used it in sparring or a real fight? Let me know.
I use it in coordinating breathing with body dynamics or body motion; which is a lot of what tai chi chuan practice is about.
The point of the training is to establish a full connection all the way from the ground to your striking surface (for example the palm of the hand) and all of the joint and muscle connections in between. The body movement goes from a contracted position (closing down through the core, loading into the hips and legs) to an expanded position (opening through the core, hips, legs, etc., driving the feet into the ground and rooting, maintaining a good base). In coordination with this body movement we inhale on the contraction (the yin part of the cycle) and exhale on the expansion (the yang part of the cycle).
As part of the inhalation, we draw in at the core and expand the rib cage (using and training the intercostal muscles, ultimately improving breathing efficiency). The analogy on this inhalation is drawing the string on a bow (bow and arrow). So, it's a complete loading of the body; muscles, skeletal structure, and breath. The analogy on the exhalation is the release of the string on the bow, the sudden release of all the energy stored up during the inhalation. In tai chi chuan this is what's known as fa jin, or the release of explosive power.
This seems like a very meticulous and detailed approach to training something that many people (particularly athletes) may actually do quite naturally. But the average person is not an athlete and doesn't normally coordinate their movements and breathing very well. And that's what this training helps with. And that's why tai chi chuan moves so slowly (most of the time), to allow for a focused training on this sort of coordination.
As for me using it in sparring and/or real fighting, most of the sparring I did was in my younger days (I'm 51 now) when I was doing light contact tournament fighting (karate competitions, before I ever started training in tai chi chuan). I try to avoid real fights. In looking back at what I was doing in that earlier light contact sparring, I believe I was actually doing this sort of breathing without being consciously aware of it. I think if I had been consciously aware of it at the time, and trained it consciously, it would have helped both my speed and power.
These days, I play with this breathing approach primarily as part of my shadow boxing, which I do for several hours each week as a piece of my overall training. So I can only speak to how it feels within the context of my shadow boxing. And it feels like it works very well.
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